FOS and obesity due to melanocortin 4 receptor deficiency: Previous studies have confirmed that AP-1 can regulate gene expression in response to various external signals and is closely related to the regulation of various cellular processes, such as cell differentiation, proliferation, and apoptosis.40Hasenfuss et al reported that AP-1 was involved in acute stress response and fat metabolism in the liver under the form of a leucine zipper, which is an effective regulator of lipid metabolism and NAFLD development and plays an important role in obesity, liver lipid metabolism, and NAFLD.41